The present invention relates to the guidance and control of missiles and projectiles and, more particularly, to a method and system for automatically compensating for the effects of gravity on a guided missile or projectile in flight.
The primary effect of gravity on the guidance of missiles or projectiles is modification of the trajectory or flight path downward from that which would be achieved in the absence of gravity. Consequential effects include increased risk of missile or projectile impact on the ground or on near-ground obstructions prior to reaching the intended target, increased requirements on missile or projectile maneuver capability in order to correct the modified trajectory, and degraded accuracy of missile or projectile impact point relative to the intended impact point on the target. These effects are sufficiently severe in many situations as to require incorporation of some means of gravity compensation in the missile or projectile guidance and control system.
Conventional techniques for gravity compensation in guided missiles or projectiles require prelaunch establishment of a known roll attitude reference (e.g., spinup of a gyroscope at a known orientation) and maintenance of that reference throughout launch and flight. The roll attitude of the missile or projectile relative to that reference is then measured by some angular sensor (e.g., a gimbal potentiometer) and the measured roll angle signal is employed either to resolve a fixed gravity bias signal into appropriate gravity compensation signals in a rolling missile or projectile, or to cause control of the missile or projectile to a particular roll attitude for which fixed gravity compensation is provided. Disadvantages of these conventional techniques include the requirement for prelaunch establishment of a known roll attitude reference (inconvenient in many cases), the requirement for maintenance of that reference throughout launch and flight (difficult or impossible for cannon launch), and the lack of means for adjusting the magnitude of the gravity compensation to meet the varied needs of different trajectories.
Another known technique for gravity compensation in guided projectiles includes means for establishing a roll attitude reference after launch by use of a pitch/yaw attitude gyroscope. A roll attitude signal is derived from the pitch/yaw attitude outputs of the gyroscope and is used to control the projectile to a particular roll attitude for which fixed gravity compensation is provided. Disadvantages of this technique include potential instability resulting from pitch/yaw/roll coupling, long roll loop settling times, and the lack of means for adjusting the magnitude of the gravity compensation to meet the varied needs of different trajectories.
It is accordingly an object of the present invention to provide a novel method and system for gravity compensation in a guided projectile or missile system in which the roll attitude of the projectile or missile need not be determined.
It is another object of the present invention to provide a novel method and system for producing a gravity compensation signal for a missile or projectile while in flight and without regard to the roll attitude at which the missile or projectile is stabilized.
It is yet another object of the present invention to provide a novel method and system for compensation of gravity in a projectile or missile guidance system in which the magnitude of gravity compensation is automatically adjusted to meet the needs of a desired trajectory.
It is still another object of the present invention to provide a novel method and system for gravity compensation in a missile or projectile guidance system wherein improved accuracy, shorter roll settling time, elimination of pitch/yaw/roll coupling instability problems and increased tolerance of guidance system parameter deviations are achieved.
It is a further object of the present invention to provide a novel method and system for producing gravity compensation signals for an in flight guided projectile or missile in which the missile or projectile is roll stabilized at an arbitrary roll attitude and pitch and yaw steering command correction signals for gravity compensation are automatically calculated at the arbitrary roll attitude in response to sensed differences between an attitude reference axis established in the missile or projectile and the attitude of the missile or projectile.